1. Field of the Invention
The present invention relates to laminography, more particularly to a method for minimizing the interference caused by dense objects or portions thereof while less dense objects are being processed.
2. Description of the Related Art
U.S. Pat. No. 6,628,745, issued to the applicants hereof, discloses a method of producing Laminography (planar) images using a rapidly moving fan beam x-ray source and a U-shaped array of detectors. The apparatus described therein is shown in the FIG. 1 and described below.
The prior state-of-the-art Laminography algorithms simply add up the intensities of the beams of x-rays from the source of the traveling fan beam 12, for each successive location of the source, that intersects the source 14, the pixel to be focused 16 and the detector 18 being sampled. Two typical rays that meet this criterion are shown in FIG. 1 as AA′ and BB′. These rays correspond to different positions of the x-ray fan beam 12 as it moves transversely across the bottom of the tunnel 20. This transverse passage must occur while the object moves a very small distance longitudinally through the plane of the row of detectors and the x-ray source line 10. This algorithm results in “focusing” the desired pixel while blurring all other regions in the volume being inspected.
This algorithm works successfully to produce focused pixels and/or lines (and then planes as the object moves along the conveyor) parallel to the x-ray source line. However, the blurred or unfocussed component of the resultant image can obscure the desired row of pixels if the blurring is caused by a relatively dense object in a blurred portion of the image that extends for a substantial length in the image parallel to the source/detector line. This effect can be caused, for example by the presence of a laptop computer in a carry-on bag being inspected at an airport, causing heavy blurring throughout the image. Another example occurs in medical imaging where it may be desired to inspect the lungs or the heart. In this case, the ribs that are relatively dense and generally parallel to the detector line can cause blurring that can reduce the visibility of the lungs or the heart.